Slow-release material for synergistically repairing heavy metal and organic compound polluted soil based on modified charcoal and microorganisms and application method of slow-release material

Abstract

The invention relates to the technical field of environmental restoration, in particular to a slow-release material for synergistically restoring heavy metal and organic compound contaminated soil based on modified biochar and microorganisms and an application method thereof.The slow-release material is prepared from, by weight, 50-80 parts of modified biochar, 30-40 parts of sodium alginate, 10-20 parts of gelatin, 5-10 parts of glycerin and 3-5 parts of calcium carbonate. The multi-modified biochar is prepared from, by weight, 300-400 parts of a functional flora mixed solution and 5-10 parts of mixed nutrient elements of glucose, yeast extract and KHPO, and through the synergistic effect of the multi-modified biochar and the functional flora, efficient immobilization (the immobilization rate gt is 60%) of heavy metal (lead, cadmium and chromium) and efficient degradation (the degradation rate gt is 70%) of organic pollutants (polycyclic aromatic hydrocarbon and petroleum hydrocarbon) are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of environmental remediation, specifically to a slow-release material for the cooperative remediation of heavy metal and organic compound contaminated soil based on modified biochar and microorganisms and its application method. The present application can be widely applied to the ecological remediation of agricultural contaminated soil, industrial contaminated sites, and mining contaminated soil, etc., which contain heavy metals (such as lead, cadmium, chromium, etc.) and organic pollutants (such as polycyclic aromatic hydrocarbons, petroleum hydrocarbons, etc.). BACKGROUND

[0002] With the acceleration of industrialization and urbanization, the problem of heavy metal and organic compound contaminated soil is becoming increasingly serious, posing a significant threat to the ecological environment and human health. Currently, the remediation techniques for soil compound pollution mainly include physical remediation, chemical remediation, and biological remediation, etc. Among them, the soil remediation technology based on biochar has attracted widespread attention due to its low cost, high efficiency, and environmental friendliness.

[0003] Chinese patent CN117884098A discloses "a modified biochar capable of adsorbing heavy metal lead and a preparation method thereof". This technology uses sludge and attapulgite as raw materials to produce biochar, which is then modified by alkali, and can be used to remove lead pollution in wastewater and soil. However, this technology has the following shortcomings: first, it only targets single heavy metal lead pollution and cannot effectively handle compound pollution problems; second, the remediation mechanism is single, mainly relying on the adsorption of biochar, with limited remediation efficiency and durability; third, it lacks consideration of the microbial ecosystem and cannot form a sustained biological remediation capacity; fourth, it does not consider the synergistic effect with phytoremediation, and the ecological remediation effect is not ideal.

[0004] In addition, in the existing technology, specific microorganisms have the functions of bio-adsorption and bio-transformation of heavy metals, but microorganisms are easily affected by environmental stress during direct application, and their activity is difficult to sustain, resulting in unstable remediation effect. In the research on the cooperative remediation of biochar and microorganisms for soil heavy metal, biochar can provide a good habitat for microorganisms, but lacks long-term protection and slow-release mechanism for microorganisms, making it difficult to achieve sustained and stable remediation effect.

[0005] Therefore, there is an urgent need to develop a new type of soil remediation material and application method that can simultaneously remediate heavy metal and organic compound pollution and has long-term slow-release function, in order to achieve efficient, durable, and ecological remediation of contaminated soil. SUMMARY

[0006] The application aims at solving the problems of the prior art, and provides a slow-release material for remediation of heavy metal and organic compound contaminated soil based on modified biochar and microorganisms and an application method, so as to achieve the following technical effects: (1) simultaneously and efficiently remediate heavy metals (lead, cadmium and chromium) and organic pollutants (polycyclic aromatic hydrocarbons, petroleum hydrocarbons and the like) in soil; (2) realize persistent release and activity maintenance of microorganisms through slow-release technology; and (3) build a microorganism-biochar-plant ternary synergistic remediation system, and improve remediation efficiency and ecological restoration effect.

[0007] To achieve the above object, the application provides a slow-release material for remediation of heavy metal and organic compound contaminated soil based on modified biochar and microorganisms, which is made of the following components in parts by weight: modified biochar 50-80 parts, sodium alginate 30-40 parts, gelatin 10-20 parts, glycerol 5-10 parts, calcium carbonate 3-5 parts, functional bacterial flora mixed solution 300-400 parts, and mixed nutrient elements of glucose, yeast extract and K2HPO4 5-10 parts.

[0008] Preferably, the modified biochar is made of the following components in parts by weight: rice straw 40-50 parts, municipal sludge 30-40 parts, magnetite powder 5-10 parts, and bentonite 10-15 parts.

[0009] Preferably, the functional bacterial flora mixed solution comprises Bacillus subtilis, Acidithiobacillus ferrooxidans, Pseudomonas putida and Paenibacillus polymyxa, and the bacterial liquid concentration is 10 8 CFU / mL, and the volume ratio of the Bacillus subtilis, Acidithiobacillus ferrooxidans, Pseudomonas putida and Paenibacillus polymyxa is 2:1:2:1.

[0010] Preferably, the weight ratio of glucose, yeast extract and K2HPO4 in the mixed nutrient elements is 3:1:1.

[0011] The application further provides a method for preparing the modified biochar, which comprises the following steps:

[0012] A. crush rice straw to 3-5 mm, dry at 60℃ for 24 hours; dewater municipal sludge to a water content of 60%, sterilize at 105℃ for 4 hours; pass magnetite powder and bentonite through a 200-mesh sieve; uniformly mix according to the proportion, and immerse in 0.5-1.0% manganese chloride solution for 12 hours;

[0013] B. The mixture obtained in step A is subjected to fractional pyrolysis, the first stage being pyrolysis at 300℃ for 2 hours, the heating rate being 5℃ / min, N2 atmosphere; the second stage being pyrolysis at 550℃ for 3 hours, the heating rate being 8℃ / min, the O2 content being less than 3% under oxygen-limited conditions; and the pyrolysis is naturally cooled to room temperature after pyrolysis;

[0014] C. The material obtained in step B is sequentially soaked with 0.5M citric acid solution for 12 hours, the solid-liquid ratio being 1:10; washed with deionized water until neutral; soaked with 1.5% KOH solution for 24 hours, the solid-liquid ratio being 1:8; and washed with deionized water until the pH is stable;

[0015] D. The material obtained in step C is soaked with a mixed solution of FeCl3·6H2O and MnSO4·H2O, the Fe:Mn ratio being 3:1, and the total concentration being 0.2M; stirred at 60℃ for 6 hours; 1M NaOH is added dropwise until the pH value is 10, and stirring is continued for 4 hours; filtered, washed, and dried at 80℃ for 24 hours;

[0016] E. The material obtained in step D is treated with 1% cetyltrimethylammonium bromide solution for 2 hours; washed with deionized water for 3 times; and dried at 60℃ to obtain the modified biochar.

[0017] The application also provides a method for preparing the functional bacterial flora mixed solution, which comprises the following steps:

[0018] A. Bacillus, iron-oxidizing bacteria, Pseudomonas and Paenibacillus brasiliensis are respectively cultured: the Bacillus is cultured in LB medium at 30℃, 180rpm for 24 hours; the iron-oxidizing bacteria are cultured in 9K medium at 28℃, 150rpm for 72 hours; the Pseudomonas is cultured in MSM medium added with 0.1% petroleum hydrocarbon as a carbon source at 30℃, 180rpm for 36 hours; and the Paenibacillus brasiliensis is cultured in PVK medium at 28℃, 160rpm for 48 hours;

[0019] B. The bacterial bodies are collected by centrifugation at a speed of 6000rpm for 10 minutes;

[0020] C. The bacterial bodies are washed twice with sterile physiological saline;

[0021] D. The concentration of each bacterial solution is adjusted to 10 8 CFU / mL;

[0022] E. The Bacillus, iron-oxidizing bacteria, Pseudomonas and Paenibacillus brasiliensis are mixed according to the volume ratio of 2:1:2:1 to obtain the functional bacterial flora mixed solution.

[0023] The application also provides a method for preparing the slow-release material, which comprises the following steps:

[0024] A. Dissolve sodium alginate in sterile deionized water, heat and stir at 60°C until completely dissolved;

[0025] B. Add gelatin, glycerol, calcium carbonate, and nutritional elements, stir until uniform, cool to 40°C;

[0026] C. Add modified biochar, stir for 30 minutes;

[0027] D. Cool to 30°C, add functional bacterial flora mixture, stir gently for 10 minutes;

[0028] E. Use a syringe pump to drop the mixture into a 2% CaCl2 solution to form gel balls with a diameter of 3-4 mm;

[0029] F. Solidify in the CaCl2 solution for 2 hours;

[0030] G. Collect the gel balls by filtration, wash with sterile deionized water twice;

[0031] H. Store at 4°C for future use.

[0032] Preferably, after step H, a multi-layer encapsulation step is also included:

[0033] I. Prepare a 1.5% chitosan solution in 1% acetic acid;

[0034] J. Immerse the gel balls prepared in step H in the chitosan solution for 10 minutes;

[0035] K. Filter, then immerse in a 1% sodium tripolyphosphate solution for 5 minutes for cross-linking;

[0036] L. Wash with deionized water 3 times, store at 4°C for future use.

[0037] The application also provides a method for using the slow-release material, which includes the following steps:

[0038] A. Soil pretreatment: Determine the soil pH, organic matter, heavy metal content, and organic pollutant content; according to the pollution degree, divide the soil into light, moderate, and severe pollution areas; add lime or sulfur to adjust the soil pH to 6.5-7.5;

[0039] B. Slow-release material application: for light pollution soil, the application amount is 50-100 g / m²; for moderate pollution soil, the application amount is 100-200 g / m²; for severe pollution soil, the application amount is 200-300 g / m²; adopt surface application method, uniformly spread on the soil surface, and slightly till 5-10 cm deep; for severe pollution areas, adopt hole application method, depth 15-20 cm; second application is performed 45-60 days after the first application;

[0040] C. Synergistic phytoremediation: For light pollution areas, plant pennisetum, density 4-6 plants / m²; for moderate pollution areas, plant sunflower, density 2-3 plants / m²; for severe pollution areas, plant alfalfa and mustard intercropping, density 10-15 plants / m²;

[0041] D. Environmental factor control: maintain soil temperature at 20-30℃, cover with mulch in winter; control soil moisture content to maintain 60-70% of field water holding capacity; loosen the soil if necessary to improve soil aeration;

[0042] E. Regular monitoring: monitor the content of heavy metals and organic pollutants in soil and plants every 30 days to evaluate the remediation effect.

[0043] Preferably, the regular monitoring includes: heavy metal removal rate monitoring, including lead, cadmium, chromium removal rate; organic pollutant degradation rate monitoring, including petroleum hydrocarbon and polycyclic aromatic hydrocarbon degradation rate; microbial activity evaluation, including functional flora number, dehydrogenase, catalase, phosphatase activity determination; ecological restoration evaluation, including plant height, biomass, photosynthetic efficiency, soil organic matter content, pH value, nutrient content, soil animal number and diversity.

[0044] The modified biochar and microorganism-based remediation of heavy metal and organic compound contaminated soil provided by the present application has the following beneficial effects:

[0045] 1. High remediation efficiency: through the synergistic effect of multiple modified biochar and functional flora, efficient fixation of heavy metals (lead, cadmium, chromium) (fixation rate >60%) and efficient degradation of organic pollutants (polycyclic aromatic hydrocarbons, petroleum hydrocarbons) (degradation rate >70%) are achieved;

[0046] 2. Good remediation durability: through the sodium alginate-gelatin-glycerin ternary slow-release system, slow release and long-term activity maintenance of microorganisms are achieved, significantly prolonging the remediation period to 45-60 days;

[0047] 3. Wide application range: capable of simultaneously treating heavy metal and organic compound contamination, suitable for soil remediation of different pollution levels;

[0048] 4. Good ecological remediation effect: through the microbial-biochar-plant ternary synergistic remediation system, not only the removal of pollutants is achieved, but also the improvement of soil ecological environment, promotion of plant growth and restoration of soil biodiversity;

[0049] 5. Wide material sources and low cost: using agricultural waste (rice straw) and municipal sludge and other waste as raw materials, resource recycling is achieved, with good economic and environmental benefits. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 A stability comparison chart of the slow-release material of the present application under different pH conditions.

[0051] Figure 2 A microbial release kinetics chart of the slow-release material of the present application. DETAILED DESCRIPTION

[0052] The present application will be further described in detail below with specific examples and Figures 1-2 The present application will be further described in detail below with specific examples and

[0053] The slow-release material for the remediation of heavy metal and organic compound contaminated soil based on modified biochar and microorganisms provided by the present application is characterized in that high-performance biochar is prepared through multiple modification strategies, combined with specific functional flora, and a microorganism-biochar composite is constructed through a sodium alginate-gelatin-glycerol ternary slow-release system, so as to realize the synergistic remediation of heavy metals and organic pollutants.

[0054] The modified biochar is a key component of the present application, and its preparation process includes multiple steps such as raw material selection, pretreatment, pyrolysis and functional modification, each of which has an important influence on the performance of the final product.

[0055] In the present application, rice straw, municipal sludge, magnetite powder and bentonite are selected as raw materials. Rice straw is rich in cellulose, hemicellulose and lignin, and can form a porous structure after pyrolysis, providing a good habitat for microorganisms; municipal sludge contains rich organic matter and various trace elements, which can increase the specific surface area and the number of functional groups of biochar; magnetite powder can enhance the adsorption capacity of biochar for heavy metals, especially for anionic heavy metals (such as chromate); bentonite has good ion exchange capacity and swelling property, which can enhance the cation exchange capacity of biochar. The synergistic effect of these raw materials makes the prepared biochar have excellent adsorption performance and microbial carrier performance.

[0056] In the present application, a segmented pyrolysis process is adopted. First, pyrolysis is carried out at 300℃ for 2 hours, the main purpose of which is to remove volatile substances in the raw materials while retaining part of the functional groups; then pyrolysis is carried out at 550℃ for 3 hours to further carbonize the materials and form a stable carbon structure. The entire pyrolysis process is carried out under controlled oxygen conditions to ensure that the material is not completely oxidized and maintains a good pore structure and specific surface area.

[0057] In the present application, three-step functional modification is carried out on the primary biochar:

[0058] Firstly, through the acid-base alternating treatment of citric acid and KOH, on the one hand, the impurities on the surface of the biochar are removed and the porosity is increased; on the other hand, more oxygen-containing functional groups (such as carboxyl and hydroxyl groups) are introduced to enhance the coordination ability for heavy metals.

[0059] Secondly, by iron / manganese oxide loading, a Fe-Mn composite oxide layer is formed on the surface of the biochar. Fe-Mn composite oxide has excellent redox performance and can reduce the highly toxic Cr(VI) to low-toxicity Cr(III), while enhancing the adsorption capacity for other heavy metals.

[0060] Finally, by treating with cetyltrimethylammonium bromide (CTAB), the hydrophobicity and cation exchange capacity of the biochar surface are increased, and the adsorption capacity for organic pollutants (such as polycyclic aromatic hydrocarbons, petroleum hydrocarbons) is improved.

[0061] Through the above multi-step functional modification, the prepared biochar can not only efficiently adsorb heavy metals, but also adsorb organic pollutants, and at the same time provide a good carrier environment for microorganisms.

[0062] The present application selects four functional strains, which are respectively aimed at different types of pollutants and repair mechanisms:

[0063] Bacillus subtilis CGMCC 1.3358: has strong heavy metal tolerance and transformation ability, can produce exopolysaccharide and metal binding protein, and can fix heavy metals through biosorption, bioprecipitation and other ways, especially has high removal efficiency for lead and cadmium. At the same time, the strain can produce various extracellular enzymes to promote the degradation of organic matter.

[0064] Acidithiobacillus ferrooxidans ATCC 23270: can oxidize Fe(II) to Fe(III) to form iron hydroxide precipitate, and remove heavy metals through coprecipitation mechanism. In addition, Fe(III) can also act as an electron acceptor to promote the degradation of certain organic matter.

[0065] Pseudomonas putida CGMCC 1.1819: has the ability to degrade a variety of organic pollutants, especially has high degradation efficiency for polycyclic aromatic hydrocarbons and petroleum hydrocarbons. The strain can produce biosurfactants to increase the bioavailability of organic pollutants.

[0066] Paenibacillus polymyxa ACCC 10252: has strong phosphorus solubilization ability, can solubilize insoluble phosphate in soil, release soluble phosphorus, and promote plant growth. At the same time, the solubilized phosphate can form insoluble phosphate precipitate with heavy metals to further fix heavy metals.

[0067] The four strains synergize with each other to form a complete functional bacterial network, which jointly acts on the remediation process of heavy metals and organic pollutants.

[0068] The present application adopts a sodium alginate-gelatin-glycerin ternary sustained-release system, constructs a microorganism-biochar composite sustained-release body through ion gelation and multi-layer encapsulation technology.

[0069] Sodium alginate is a natural polysaccharide, which can quickly gelate in the presence of Ca²⁺ to form a stable three-dimensional network structure; gelatin is a natural protein with good film-forming property and biocompatibility, which can enhance the mechanical strength of the gel; glycerin as a plasticizer can increase the elasticity and water retention of the gel to prevent microbial dehydration inactivation.

[0070] The addition of calcium carbonate can neutralize the acidic substances produced by microbial metabolism, maintain a suitable pH environment; on the other hand, calcium carbonate will slowly dissolve under acidic conditions in soil, releasing Ca²⁺ to strengthen the gel structure and prolong the sustained-release effect.

[0071] Nutritional elements (glucose, yeast extract and K2HPO4) provide carbon source, nitrogen source and phosphorus source required for initial growth of microorganisms, ensuring that microorganisms can quickly recover activity in the initial release period.

[0072] Multi-layer encapsulation (chitosan-sodium tripolyphosphate crosslinking) further enhances the mechanical strength and stability of the sustained-release body, prolongs the release time and activity maintenance time of the microorganisms.

[0073] The application method of the present application considers the characteristics and needs of different pollution levels of soil, adopts a regional and phased treatment strategy, and combines with phytoremediation to construct a complete microorganism-biochar-plant ternary synergistic remediation system.

[0074] For different pollution levels of soil, different application amounts and application methods are adopted to ensure the remediation effect while reducing the remediation cost. For severely contaminated areas, hole application method is adopted to directly apply the sustained-release material to the soil layer with high concentration of pollutants to improve the remediation efficiency.

[0075] Synergistic phytoremediation is an important feature of the present application. Wolf tail grass, sunflower, alfalfa and mustard plants not only can absorb part of the heavy metals, but also can activate soil microorganisms through root exudates to promote the degradation and transformation of pollutants. At the same time, the growth of plants improves the soil structure and ecological environment, and promotes the recovery of soil ecosystem.

[0076] Environmental factor control and regular monitoring ensure the stability and controllability of the remediation process, providing a scientific basis for remediation effect evaluation and adjustment.

[0077] Example 1: Preparation of modified biochar

[0078] Rice straw was crushed to 3 mm and dried at 60 °C for 24 h. Municipal sludge (moisture content of about 75%) was dewatered to a moisture content of 60% and sterilized at 105 °C for 4 h. Magnetite powder (purity > 98%, particle size < 100 μm) and bentonite (sodium-based bentonite, CEC > 80 meq / 100 g) were sieved through a 200 mesh sieve. The mixture was prepared according to the ratio of 40 parts of rice straw, 30 parts of municipal sludge, 5 parts of magnetite powder, and 10 parts of bentonite. The mixture was impregnated with 0.5% manganese chloride solution (analytical pure, National Pharmaceutical Group Chemical Reagent Co., Ltd.) for 12 h, with a solid-liquid ratio of 1:5.

[0079] The mixture was subjected to stepwise pyrolysis in a tube furnace: first pyrolysis at 300 °C for 2 h, with a heating rate of 5 °C / min, and high-purity nitrogen (purity > 99.999%) was introduced; then pyrolysis at 550 °C for 3 h, with a heating rate of 8 °C / min, and oxygen was limited (O2 content controlled at about 2%); after pyrolysis, the sample was naturally cooled to room temperature.

[0080] The obtained primary biochar was soaked in 0.5 M citric acid solution (food grade) for 12 h, with a solid-liquid ratio of 1:10; washed with deionized water until neutral; then soaked in 1.5% KOH solution (analytical pure, National Pharmaceutical Group Chemical Reagent Co., Ltd.) for 24 h, with a solid-liquid ratio of 1:8; washed with deionized water until the pH stabilized at 6.5-7.5.

[0081] The above treated biochar was soaked in a mixed solution of FeCl3·6H2O (analytical pure) and MnSO4·H2O (analytical pure), with a Fe:Mn ratio of 3:1 and a total concentration of 0.2 M; stirred at 60 °C for 6 h; added 1 M NaOH dropwise to pH 10 and continued to stir for 4 h; filtered, washed, and dried at 80 °C for 24 h.

[0082] Finally, the above material was treated with 1% cetyltrimethylammonium bromide (CTAB, analytical pure, Shanghai Aladdin Biochemical Technology Co., Ltd.) solution for 2 h; washed with deionized water for 3 times; dried at 60 °C to obtain modified biochar.

[0083] The prepared modified biochar was characterized: the specific surface area (BET method) was 785.3 m² / g, the pore volume was 1.23 cm³ / g, and the average pore size was 3.6 nm; SEM observation showed that the surface was porous with developed pores; XRD analysis confirmed the successful loading of Fe-Mn oxides; FT-IR analysis showed that the surface contained abundant oxygen-containing functional groups (-OH, -COOH, etc.).

[0084] Example 2: Cultivation and preparation of functional bacterial flora

[0085] Cultivation of Bacillus subtilis CGMCC 1.3358:

[0086] Bacillus subtilis CGMCC 1.3358 was inoculated into LB liquid medium (10 g / L of proteose peptone, 5 g / L of yeast extract, 10 g / L of NaCl, pH 7.0-7.2, autoclaved at 121°C for 20 minutes) and cultured at 30°C and 180 rpm for 24 hours.

[0087] Culture of Acidithiobacillus ferrooxidans ATCC 23270:

[0088] Acidithiobacillus ferrooxidans ATCC 23270 was inoculated into 9K medium [(NH4)2SO4 3.0 g / L, KCl 0.1 g / L, K2HPO4 0.5 g / L, MgSO4·7H2O 0.5 g / L, Ca(NO3)2 0.01 g / L, FeSO4·7H2O 44.22 g / L, pH 2.0-2.5, autoclaved at 121°C for 20 minutes] and cultured at 28°C and 150 rpm for 72 hours.

[0089] Culture of Pseudomonas putida CGMCC 1.1819:

[0090] Pseudomonas putida CGMCC 1.1819 was inoculated into MSM medium [KH2PO4 0.5 g / L, K2HPO4 0.5 g / L, CaCl2 0.1 g / L, MgSO4·7H2O 0.2 g / L, NH4NO3 1.0 g / L, FeCl3 0.05 g / L, pH 7.0-7.2, autoclaved at 121°C for 20 minutes] supplemented with 0.1% petroleum hydrocarbon (analytically pure, Shanghai Aldrich Biochemical Technology Co., Ltd.) as a carbon source and cultured at 30°C and 180 rpm for 36 hours.

[0091] Culture of Paenibacillus polymyxa ACCC 10252:

[0092] Paenibacillus polymyxa ACCC 10252 (inoculated in PVK medium [glucose 10 g / L, (NH4)2SO4 0.5 g / L, NaCl 0.3 g / L, KCl 0.3 g / L, MgSO4·7H2O 0.3 g / L, FeSO4·7H2O 0.03 g / L, MnSO4·H2O 0.03 g / L, hydroxyapatite 10 g / L, pH 7.0-7.2, autoclaved at 121℃ for 20 minutes]) was cultured at 28℃, 160 rpm for 48 hours.

[0093] After each bacterial liquid culture was completed, the bacterial cells were collected by centrifugation (6000 rpm, 10 minutes), washed twice with sterile normal saline (0.85% NaCl), and the concentration of each bacterial liquid was adjusted to 10 8 CFU / mL (using plate counting and optical density method OD 600 measurement). Bacillus, iron-oxidizing bacteria, Pseudomonas and Paenibacillus were mixed in a volume ratio of 2:1:2:1 to obtain a functional bacterial community mixture.

[0094] Example 3: Preparation of slow-release material

[0095] Dissolve 30 g of sodium alginate (food grade, viscosity ≥ 600 mPa·s, M / G ratio of 1.5) in 900 mL of sterile deionized water, heat and stir at 60℃ until completely dissolved; add 10 g of gelatin (food grade, bloom value 250-300), 5 g of glycerol (analytical pure), 3 g of calcium carbonate (analytical pure, National Pharmaceutical Group Chemical Reagent Co., Ltd.), 5 g of mixed nutrient elements (glucose 3 g, yeast extract 1 g, K2HPO4 1 g), stir uniformly, and cool to 40℃; add 50 g of modified biochar prepared in Example 1, stir for 30 minutes; cool to 30℃, add 300 g of functional bacterial community mixture prepared in Example 2, and stir gently for 10 minutes.

[0096] Use a syringe pump (constant flow pump, BT100-1L) to drop the mixture through a needle with an inner diameter of 1.5 mm into a 2% CaCl2 solution (analytical pure), with a drop rate of 2-3 drops per second, forming gel balls with a diameter of 3-4 mm; solidify in the CaCl2 solution for 2 hours; collect the gel balls by filtration, wash twice with sterile deionized water; store the gel balls at 4℃ for standby use.

[0097] To improve the stability of the slow-release material, multi-level encapsulation treatment was performed: a 1.5% chitosan solution (chitosan, degree of deacetylation ≥ 90%, molecular weight 50-190 kDa) was prepared by dissolving in 1% acetic acid (analytical pure); the gel balls were immersed in the chitosan solution for 10 minutes; filtration was performed, and then cross-linking was performed by immersing in a 1% sodium tripolyphosphate (analytical pure) solution for 5 minutes; deionized water was used for washing 3 times, and the product was stored at 4°C for standby use.

[0098] The prepared slow-release material was spherical with a diameter of about 3.5 mm, smooth surface, uniform texture, and light brown color. SEM observation showed that the modified biochar was uniformly distributed in the gel network, and the microorganisms were attached to the surface and pores of the biochar.

[0099] Example 4: Preparation of slow-release materials with different component allocation ratios

[0100] According to the method of Example 3, slow-release materials with different component allocation ratios were prepared, and the specific formulations were as follows:

[0101] Slow-release material A: modified biochar 50 g, sodium alginate 30 g, gelatin 10 g, glycerol 5 g, calcium carbonate 3 g, functional bacterial group mixed solution 300 g, and mixed nutrient elements 5 g.

[0102] Slow-release material B: modified biochar 65 g, sodium alginate 35 g, gelatin 15 g, glycerol 7.5 g, calcium carbonate 4 g, functional bacterial group mixed solution 350 g, and mixed nutrient elements 7.5 g.

[0103] Slow-release material C: modified biochar 80 g, sodium alginate 40 g, gelatin 20 g, glycerol 10 g, calcium carbonate 5 g, functional bacterial group mixed solution 400 g, and mixed nutrient elements 10 g.

[0104] Example 5: Preparation of slow-release materials with different component allocation ratios of modified biochar

[0105] According to the method of Example 1, modified biochar with different raw material ratios was prepared, and then according to the method of Example 3, slow-release materials were prepared, as follows:

[0106] Modified biochar D: rice straw 40 parts, municipal sludge 30 parts, magnetite powder 5 parts, and bentonite 10 parts.

[0107] Modified biochar E: rice straw 45 parts, municipal sludge 35 parts, magnetite powder 7.5 parts, and bentonite 12.5 parts.

[0108] Modified biochar F: rice straw 50 parts, municipal sludge 40 parts, magnetite powder 10 parts, and bentonite 15 parts.

[0109] The modified biochar D, E and F described above is used to replace the modified biochar in Example 3, and other components and steps are unchanged to prepare the slow-release material D, E and F.

[0110] Example 6: Preparation of slow-release material of different functional bacterial flora combinations

[0111] According to the method of Example 2, each functional strain is cultured, and a functional bacterial flora mixture is prepared by mixing in different proportions, and then a slow-release material is prepared according to the method of Example 3, as follows:

[0112] The functional bacterial flora mixture G: the volume ratio of Bacillus, iron-oxidizing bacteria, Pseudomonas and Paenibacillus brasiliensis is 1:1:1:1.

[0113] The functional bacterial flora mixture H: the volume ratio of Bacillus, iron-oxidizing bacteria, Pseudomonas and Paenibacillus brasiliensis is 3:1:3:1.

[0114] The functional bacterial flora mixture I: the volume ratio of Bacillus, iron-oxidizing bacteria, Pseudomonas and Paenibacillus brasiliensis is 2:0:2:1 (without iron-oxidizing bacteria).

[0115] The functional bacterial flora mixture J: the volume ratio of Bacillus, iron-oxidizing bacteria, Pseudomonas and Paenibacillus brasiliensis is 2:1:0:1 (without Pseudomonas).

[0116] The functional bacterial flora mixture G, H, I and J described above is used to replace the functional bacterial flora mixture in Example 3, and other components and steps are unchanged to prepare the slow-release material G, H, I and J.

[0117] Example 7: Application method of slow-release material

[0118] Soil pretreatment:

[0119] Heavy metal and organic compound contaminated soil around an industrial area is collected, air-dried and sieved (2 mm sieve), and its basic physicochemical properties are determined: pH 5.8, organic matter content 1.2%, total lead content 385 mg / kg, total cadmium content 4.2 mg / kg, total chromium content 128 mg / kg, petroleum hydrocarbon content 1250 mg / kg, and polycyclic aromatic hydrocarbon content 65 mg / kg. According to the national soil environmental quality standard (GB 15618-2018), the soil belongs to moderately contaminated soil. Lime (analytical pure, National Pharmaceutical Group Chemical Reagents Co., Ltd.) is added to the soil to adjust the pH to 7.0.

[0120] Slow-release material application:

[0121] The slow-release material prepared in Example 3 was uniformly applied to the surface of the treated soil at a dosage of 150 g / m2, and was lightly plowed to a depth of 8 cm to fully mix the slow-release material with the soil. The second application was performed 50 days after the first application at a dosage of 100 g / m2.

[0122] Synergistic phytoremediation:

[0123] Sunflower (variety: Jingyou No. 9, Oil Crop Research Institute of Chinese Academy of Agricultural Sciences) was selected as the remediation plant and was planted at a density of 2.5 plants / m2. Before planting, the sunflower seeds were sterilized with a 0.1% potassium permanganate solution for 10 minutes, rinsed with sterile water three times, and sowed after being soaked in the dark at 25°C for 24 hours.

[0124] Environmental factor control:

[0125] The test was conducted in a greenhouse with a temperature controlled at 25±3°C and a relative humidity of 65±5%. The soil water content was controlled at 65% of the field water holding capacity by weighing method. The soil was loosened every 10 days to improve soil aeration.

[0126] Regular monitoring:

[0127] Soil and plant samples were collected every 30 days to determine the heavy metal content (atomic absorption spectrophotometry, AA-7000, Shimadzu Corporation), organic pollutant content (gas chromatography-mass spectrometry, GCMS-QP2020, Shimadzu Corporation), microbial quantity (plate count method), soil enzyme activity (TTC method for dehydrogenase activity, potassium permanganate titration method for catalase activity, and disodium p-nitrophenyl phosphate method for phosphatase activity), and plant growth indicators (plant height and biomass).

[0128] Example 8: Comparison of application effects of slow-release materials with different dosages

[0129] According to the method of Example 7, the same batch of contaminated soil was treated with slow-release materials (prepared in Example 3) at different dosages as follows:

[0130] Treatment K: The slow-release material was applied at a dosage of 75 g / m2, and the second application was performed 50 days after the first application at a dosage of 50 g / m2.

[0131] Treatment L: The slow-release material was applied at a dosage of 150 g / m2, and the second application was performed 50 days after the first application at a dosage of 100 g / m2 (same as Example 7).

[0132] Treatment M: The slow-release material was applied at a dosage of 225 g / m2, and the second application was performed 50 days after the first application at a dosage of 150 g / m2.

[0133] Example 9: Comparison of remediation effects of different pollution levels of soil

[0134] The method of Example 7 was followed to treat soils of different pollution levels with the same amount of slow-release material (prepared in Example 3), as follows:

[0135] Mildly polluted soil: pH 6.2, organic matter content 1.5%, total lead content 180 mg / kg, total cadmium content 1.8 mg / kg, total chromium content 65 mg / kg, petroleum hydrocarbon content 650 mg / kg, polycyclic aromatic hydrocarbon content 28 mg / kg. The amount of slow-release material was 75 g / m2, and the second application was performed 50 days after the first application at a dosage of 50 g / m2. The companion plant was selected to be Pennisetum alopecuroides, with a density of 5 plants / m2.

[0136] Moderately polluted soil: same as Example 7.

[0137] Heavily polluted soil: pH 5.5, organic matter content 0.9%, total lead content 720 mg / kg, total cadmium content 8.5 mg / kg, total chromium content 256 mg / kg, petroleum hydrocarbon content 2850 mg / kg, polycyclic aromatic hydrocarbon content 135 mg / kg. The amount of slow-release material was 225 g / m2, and the second application was performed 50 days after the first application at a dosage of 150 g / m2. The companion plant was selected to be Medicago sativa intercropped with Brassica juncea, with a total density of 12 plants / m2.

[0138] Example 10: Effect of microbial-biochar-plant ternary synergistic remediation

[0139] The polluted soil and slow-release material dosage of Example 7 were used to set up different treatment combinations to evaluate the effect of ternary synergistic remediation:

[0140] Treatment N: only slow-release material was applied, without planting plants.

[0141] Treatment O: only sunflowers were planted, without applying slow-release material.

[0142] Treatment P: slow-release material was applied and sunflowers were planted (same as Example 7).

[0143] Comparative Example 1: Preparation and application of slow-release material using unmodified biochar

[0144] Rice straw and municipal sludge were mixed in a mass ratio of 4:3, and pyrolysis was directly performed (550°C, 3 hours) without functional modification to obtain unmodified biochar. According to the method of Example 3, unmodified biochar was used to replace modified biochar, and other components and steps were unchanged to prepare slow-release material Q. According to the method of Example 7, it was applied to the same polluted soil.

[0145] Preparation and application of slow-release material without functional flora

[0146] According to the method of Example 3, sterile normal saline was used instead of the functional flora mixture, and other components and steps were unchanged, to prepare slow-release material R. According to the method of Example 7, it was applied to the same contaminated soil.

[0147] Example 3: Preparation and application of slow-release material with functional flora

[0148] The modified biochar prepared in Example 1 was directly mixed with the functional flora mixture prepared in Example 2 (without sodium alginate encapsulation), and was directly applied to the same contaminated soil in the same amount as Example 7.

[0149] Preparation and application of slow-release material without functional flora

[0150] According to the method of Example 2, Bacillus subtilis CGMCC 1.3358 was cultured, and according to the method of Example 3, Bacillus liquid was used instead of the functional flora mixture, and other components and steps were unchanged, to prepare slow-release material S. According to the method of Example 7, it was applied to the same contaminated soil.

[0151] Preparation and application of modified biochar in Comparative Document 1

[0152] According to the method of CN117884098A, attapulgite and sludge were used as raw materials, and after the biochar was fired and modified with NaOH, modified biochar T was obtained. Modified biochar T was directly applied to the contaminated soil of Example 7, and the amount was the same as Example 7.

[0153] Test results and analysis are as follows:

[0154] 1. Comparison of heavy metal fixation effect of slow-release material

[0155] Table 1 Effect of different treatments on available content of heavy metals in soil (unit: mg / kg)

[0156] Treatment Lead (initial value: 135.6) Cadmium (initial value: 2.8) Chromium (initial value: 45.2) 30 days 60 days 90 days 30 days 60 days 90 days 30 days 60 days 90 days Example 7 (Treatment L) 98.7 54.2 38.5 1.9 1.2 0.8 30.8 21.3 16.7 Treatment K 110.3 76.5 62.8 2.2 1.7 1.4 36.5 28.9 24.3 Treatment M 85.4 42.8 28.6 1.6 0.9 0.6 26.2 17.4 12.1 Comparative Example 1 125.8 115.6 108.3 2.6 2.4 2.2 42.7 40.2 38.5 Comparative Example 2 115.2 98.3 85.7 2.4 2.1 1.8 38.4 33.6 30.2 Comparative Example 3 108.5 84.2 79.6 2.3 1.9 1.7 36.2 31.5 28.3 Comparative Example 4 112.3 87.5 72.4 2.3 1.8 1.5 37.8 32.4 27.5 Comparative Example 5 118.7 103.2 94.5 2.5 2.2 2 40.1 37.3 35.2 Blank control 136.2 134.8 133.5 2.8 2.7 2.7 45.5 44.8 44.2

[0157] As can be seen from Table 1, the slow-release material of the present application has a significant immobilization effect on heavy metals in the soil. After 90 days, the available content of lead, cadmium and chromium in Example 7 (treatment L) is reduced by 71.6%, 71.4% and 63.1% respectively, which is much higher than Comparative Examples 1-5 and the blank control. With the increase of the amount of slow-release material (treatment K→L→M), the heavy metal immobilization effect is also gradually enhanced. This result shows that the synergistic immobilization effect of the multiple modified biochar, functional bacterial flora combination and slow-release system of the present application on heavy metals is obviously better than single component or traditional methods.

[0158] 2. Comparison of the degradation effect of the slow-release material on organic pollutants

[0159] Table 2 Effect of different treatments on the content of organic pollutants in the soil (unit: mg / kg)

[0160] Treatment Petroleum hydrocarbon (initial value: 1250) Polycyclic aromatic hydrocarbon (initial value: 65) 30 days 60 days 90 days 30 days 60 days 90 days Example 7 875 462 187 48.2 29.5 14.3 Treatment K 965 625 312 53.6 38.4 22.5 Treatment M 820 385 125 45.3 24.8 9.8 Comparative Example 1 1125 985 865 61.2 57.8 53.5 Comparative Example 2 1085 928 750 59.5 53.2 45.8 Comparative Example 3 935 625 385 52.3 38.5 28.6 Comparative Example 4 1065 876 718 58.7 52.1 44.3 Comparative Example 5 1182 1087 962 62.8 59.7 56.2 Blank control 1235 1215 1185 64.5 63.8 62.5

[0161] Table 2 shows that the slow-release material of the present application also has a significant degradation effect on organic pollutants. After 90 days, the degradation rates of petroleum hydrocarbons and polycyclic aromatic hydrocarbons in Example 7 (treatment L) are 85.0% and 78.0% respectively, which is obviously better than Comparative Examples 1-5 and the blank control. In particular, compared with Comparative Example 2 and Comparative Example 4, it shows that the combination of functional bacterial flora plays a key role in the degradation of organic pollutants; compared with Comparative Example 3, it shows that the slow-release system can effectively protect the microbial activity and prolong the degradation effect.

[0162] 3. Changes in the number and activity of microorganisms

[0163] Table 3 Changes in the number and enzyme activity of microorganisms in the soil of different treatments

[0164] Treatment Total bacteria count (x 10 7 CFU / g) Dehydrogenase activity (μg TPF / g-h) 30 days 60 days 90 days 30 days 60 days 90 days Example 7 8.5 12.3 9.8 24.5 32.6 28.4 Treatment P 9.2 14.5 11.2 26.8 35.2 30.5 Treatment N 7.8 10.5 8.2 22.3 28.7 25.1 Treatment O 3.2 4.5 3.8 10.2 12.5 11.3 Comparative Example 1 3.5 4.8 4.1 11.5 13.8 12.2 Comparative Example 2 2.8 3.2 2.5 9.2 10.5 8.7 Comparative Example 3 6.2 5.3 2.1 18.5 15.2 8.3 Comparative Example 5 2.3 2.6 2.2 8.6 9.4 8.1 Blank control 1.8 1.9 1.7 7.2 7.5 7

[0165] Table 3 shows that the slow-release material of the present application can significantly increase the number and activity of microorganisms in the soil. Example 7 (treatment L) reaches the peak of the number and enzyme activity of microorganisms at 60 days, and then slightly decreases but still maintains at a high level. Compared with Comparative Example 3, the slow-release system of the present application can maintain the long-term activity of microorganisms; compared with treatment N and treatment O, the ternary synergistic system of microorganisms-biochar-plants (treatment P) has the best effect, which shows that there is a synergistic effect among the three.

[0166] 4. Plant growth conditions and heavy metal accumulation

[0167] Table 4 Effect of different treatments on the growth of sunflower and the accumulation of heavy metals (90 days)

[0168] Treatment Plant height (cm) Aboveground biomass (g / plant) Lead content (mg / kg) Cadmium content (mg / kg) Chromium content (mg / kg) Example 7 135.6 285.3 15.2 0.42 3.8 Treatment K 125.3 262.5 18.5 0.53 4.6 Treatment M 142.8 305.6 12.3 0.35 3.2 Treatment O 85.2 165.3 35.6 1.25 8.7 Comparative Example 1 98.5 198.2 28.3 0.98 7.2 Comparative Example 2 95.3 185.6 30.1 1.05 7.5 Comparative Example 3 110.2 225.3 23.5 0.85 6.3 Comparative Example 4 105.6 215.8 25.2 0.92 6.8 Comparative Example 5 92.5 178.3 32.6 1.12 7.8

[0169] Table 4 shows that the slow-release material of the present application can effectively promote plant growth while reducing the absorption and accumulation of heavy metals by plants. The sunflower height and biomass of Example 7 (treatment L) were 59.2% and 72.6% higher than those of treatment O (only planting sunflower), respectively, while the lead, cadmium, and chromium contents were reduced by 57.3%, 66.4%, and 56.3%, respectively. This indicates that the slow-release material of the present application not only fixes heavy metals in the soil, reducing their bioavailability, but also promotes plant growth by improving the soil environment.

[0170] 5. Remediation effect of different pollution degree soils

[0171] Table 5 Comparison of remediation effect of different pollution degree soils (90 days)

[0172] Degree of pollution Heavy metal fixation rate (%) Organic pollutant degradation rate (%) Plant growth condition Lead Cadmium Chromium Petroleum hydrocarbon Polycyclic aromatic hydrocarbon Plant height (cm) Biomass (g / plant) Mild pollution 82.5 85.3 75.6 92.3 88.5 142.5 315.6 Moderate pollution 71.6 71.4 63.1 85 78 135.6 285.3 Severe pollution 58.2 62.5 52.8 73.5 65.2 85.3 168.2

[0173] Table 5 shows that the slow-release material of the present application has good remediation effect on soils with different pollution degrees, but the remediation efficiency decreases with the increase of pollution degree. This is due to the increased inhibition of high-concentration pollutants on microbial activity and the increased competition between pollutants and adsorption sites. However, for heavily polluted soils, the slow-release material of the present application still shows considerable remediation effect.

[0174] By monitoring the number changes of each functional strain in the soil, the microbial release characteristics of the slow-release material were analyzed. The results show that the number of microorganisms slowly increases in the first 10 days after application; the number of microorganisms rapidly increases and maintains at a high level during 10-50 days; and the number of microorganisms slowly decreases after 50 days. This change trend is consistent with the physicochemical properties and degradation characteristics of the slow-release material, indicating that the slow-release system of the present application can achieve slow release and long-term activity maintenance of microorganisms.

[0175] Based on the above examples and test results, the slow-release material and application method for remediation of heavy metal and organic compound contaminated soil based on modified biochar and microbial synergistic remediation provided by the present application have the following technical features and advantages:

[0176] 1. The multi-modified biochar has excellent adsorption and carrier properties, which can adsorb heavy metals and organic pollutants at the same time, and provide a good habitat for microorganisms;

[0177] 2. The functional bacterial flora combination can target different types of pollutants and exert their respective remediation functions to achieve synergistic remediation effect;

[0178] 3. The sodium alginate-gelatin-glycerol ternary slow-release system can protect microorganisms, achieve their slow release and long-term activity maintenance;

[0179] 4. The microbial-biochar-plant ternary remediation system can significantly improve the remediation efficiency and improve the ecological environment of the soil.

[0180] 5. The slow-release material has good remediation effect on different pollution degrees of soil, and has wide application prospect.

[0181] Compared with the prior art, the present application has significant improvement in remediation efficiency, durability, application range and ecological friendliness, and provides a new technical path for the ecological remediation of heavy metal and organic compound contaminated soil.

[0182] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A slow-release material based on modified biochar and microorganisms for the synergistic remediation of heavy metal and organic compound contaminated soil, characterized in that, The slow-release material is made of the following components by weight: modified biochar 50-80 parts, sodium alginate 30-40 parts, gelatin 10-20 parts, glycerol 5-10 parts, calcium carbonate 3-5 parts, functional bacterial community mixed solution 300-400 parts, mixed nutrient elements of glucose, yeast extract and K2HPO4 5-10 parts.

2. The slow release material according to claim 1, wherein, The modified biochar is made of the following components by weight: rice straw 40-50 parts, municipal sludge 30-40 parts, magnetite powder 5-10 parts, bentonite 10-15 parts.

3. The slow release material according to claim 1, wherein, The functional bacterial flora mixture comprises Bacillus subtilis, Acidithiobacillus ferrooxidans, Pseudomonas putida and Paenibacillus polymyxa, and the concentration of the bacterial solution is 10 8 CFU / mL, and the volume ratio of the Bacillus subtilis, Acidithiobacillus ferrooxidans, Pseudomonas putida and Paenibacillus polymyxa is 2:1:2:

1.

4. The slow release material according to claim 1, wherein The weight ratio of glucose, yeast extract and K2HPO4 in the mixed nutrient elements is 3:1:

1.

5. A method of producing the modified biochar in the slow release material of any one of claims 1-4, characterized in that, The method comprises the following steps: A. Crush the rice straw to 3-5 mm and dry at 60℃ for 24 hours; dewater the municipal sludge to a moisture content of 60% and sterilize at 105℃ for 4 hours; pass the magnetite powder and bentonite through a 200 mesh sieve; mix uniformly according to the proportions and immerse in a 0.5-1.0% manganese chloride solution for 12 hours; B. Perform stepwise pyrolysis on the mixture obtained in step A, pyrolyze at 300℃ for 2 hours in the first stage at a heating rate of 5℃ / min in a N2 atmosphere; pyrolyze at 550℃ for 3 hours in the second stage at a heating rate of 8℃ / min under oxygen-limited conditions with O2 content less than 3%; naturally cool to room temperature after pyrolysis; C. Soak the material obtained in step B in 0.5M citric acid solution for 12 hours with a solid-liquid ratio of 1:10; wash with deionized water until neutral; soak in 1.5% KOH solution for 24 hours with a solid-liquid ratio of 1:8; wash with deionized water until the pH stabilizes; D. Soak the material obtained in step C in a mixed solution of FeCl3·6H2O and MnSO4·H2O with a Fe:Mn ratio of 3:1 and a total concentration of 0.2M; stir at a constant temperature of 60℃ for 6 hours; add 1M NaOH dropwise to a pH of 10 and continue stirring for 4 hours; filter, wash and dry at 80℃ for 24 hours; E. Treat the material obtained in step D with 1% cetyltrimethylammonium bromide solution for 2 hours; wash with deionized water 3 times; dry at 60℃ to obtain modified biochar.

6. The method for preparing the functional bacterial flora mixture solution of the sustained-release material according to any one of claims 1 to 4, characterized by, The method comprises the following steps: A. Cultivate Bacillus, iron-oxidizing bacteria, Pseudomonas and Paenibacillus brasiliensis respectively: cultivate Bacillus in LB medium at 30℃, 180rpm for 24 hours; cultivate iron-oxidizing bacteria in 9K medium at 28℃, 150rpm for 72 hours; cultivate Pseudomonas in MSM medium with 0.1% petroleum hydrocarbon as carbon source at 30℃, 180rpm for 36 hours; cultivate Paenibacillus brasiliensis in PVK medium at 28℃, 160rpm for 48 hours; B. Centrifuge to collect each bacterial cell at a speed of 6000rpm for 10 minutes; C. Wash each bacterial cell with sterile physiological saline 2 times; D. Adjust each bacterial solution to 10 8 CFU / mL; E. Mix Bacillus, iron-oxidizing bacteria, Pseudomonas and Paenibacillus brasiliensis according to a volume ratio of 2:1:2:1 to obtain a functional bacterial community mixed solution.

7. A method of preparing the slow release material according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: A. Dissolve sodium alginate in sterile deionized water and heat and stir at 60℃ until completely dissolved; B. Add gelatin, glycerol, calcium carbonate and nutrient elements, stir uniformly and cool to 40℃; C. Add modified biochar, stir for 30 minutes; D. Cool to 30℃, add functional bacteria mixture, stir gently for 10 minutes; E. Use a syringe pump to drop the mixture into a 2% CaCl2 solution to form gel balls with a diameter of 3-4mm; F. Solidify in CaCl2 solution for 2 hours; G. Collect gel balls by filtration, wash with sterile deionized water for 2 times; H. Store at 4℃ for standby.

8. The preparation method according to claim 7, characterized in that, After step H, a multi-level encapsulation step is also included: I. Prepare a 1.5% chitosan solution dissolved in 1% acetic acid; J. Immerse the gel balls prepared in step H into the chitosan solution for 10 minutes; K. Filter, then immerse in a 1% sodium tripolyphosphate solution for 5 minutes for crosslinking; L. Wash with deionized water for 3 times, store at 4℃ for standby.

9. The method of using the slow release material of any one of claims 1-4, wherein, The following steps are included: A. Soil pretreatment: Determine the soil pH, organic matter, heavy metal content, and organic pollutant content; according to the pollution degree, divide the soil into light, moderate, and severe pollution areas; add lime or sulfur to adjust the soil pH to 6.5-7.5; B. Slow-release material application: for light pollution soil, the application amount is 50-100g / m²; for moderate pollution soil, the application amount is 100-200g / m²; for severe pollution soil, the application amount is 200-300g / m²; adopt surface application method, evenly spread on the soil surface, and slightly tillage 5-10cm; for severe pollution area, adopt hole application method, depth 15-20cm; second application is carried out 45-60 days after the first application; C. Synergistic phytoremediation: for light pollution area, plant Chinese penisetum, density 4-6 plants / m²; for moderate pollution area, plant sunflower, density 2-3 plants / m²; for severe pollution area, plant alfalfa and mustard intercropping, density 10-15 plants / m²; D. Environmental factor control: maintain soil temperature at 20-30℃, cover with mulch in winter; control soil moisture content to maintain 60-70% of field water holding capacity; if necessary, loosen the soil to improve soil aeration; E. Regular monitoring: monitor heavy metal and organic pollutant content in soil and plants every 30 days to evaluate the remediation effect.

10. The method of use of claim 9, wherein, The regular monitoring includes: heavy metal removal rate monitoring, including lead, cadmium, and chromium removal rate; organic pollutant degradation rate monitoring, including petroleum hydrocarbon and polycyclic aromatic hydrocarbon degradation rate; microbial activity evaluation, including functional bacteria number, dehydrogenase, catalase, and phosphatase activity determination; ecological restoration evaluation, including plant height, biomass, photosynthetic efficiency, soil organic matter content, pH value, nutrient content, and soil animal number and diversity.

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